This invention relates generally to shoes, and more particularly to shoes wherein light weight and the ability to tailor the stiffness and flexure of the shoe is an important consideration.
Shoes encounter tremendous forces during running or sports. Over the years, efforts have been made to reduce the resultant stresses on the feet and legs. One advance in this area has been the incorporation of cushioning material in the shoe sole to absorb the impact and cushion the foot as the shoe strikes the ground. This cushioning material is typically formed into a layer called the "midsole" which is interposed between the ground-engaging "outsole" and the shoe upper. The cushioning midsole, which should also flex with the foot, is typically made of ethyl-vinyl-acetate (EVA) or polyurethane (PU), although other resilient, cushioning materials could be used.
While the cushioning provided by a midsole is an advantage, its added weight hinders the performance of athletic shoes (particularly running shoes), which must be as light as possible. The problem of added weight from the midsole is recognized in U.S. Pat. No. 5,319,866 issued to Foley et al. Foley et al. attempts to solve the problem by substituting an arch support in place of the midsole and outsole underlying the arch area of the foot.
The use of a midsole between the outsole and the upper also positions the foot higher above the ground, creating a less stable platform for the foot. This problem is addressed to some degree in U.S. Pat. No. 4,542,598 issued to Misevich et al. The Misevich shoe includes a heel plate between two heel midsole layers to support and cushion the heel, and a forefoot board inside the upper over a forefoot midsole layer to support and cushion the forefoot. As in Foley, Misevich eliminates the midsole beneath the arch, thereby saving some weight. Unlike Foley, however, Misevich does not provide any additional structure to support the arch.
The negative effects of the impact to the feet and legs can be amplified if the shoes are not properly shaped and tuned to the particular sport, and to the individual's foot. Mass-produced athletic shoes come in standard sizes and shapes, and usually include an arch support designed to fit a "standard" foot. Prior art shoes, such as those typified by Foley and Misevich, include no provision for tailoring the shoe to fit an individual foot, except for the use of orthotics. Orthotics are well-known in the art, and are exemplified by U.S. Pat. No. 4,803,747 issued to Brown. Orthotics, however useful, represent additional, undesirable weight, and also stiffen the shoe and otherwise compromise its performance.
A further disadvantage of the prior art shoes is that they cannot be readily "tuned" to meet the particular needs of the wearer. This is particularly important for athletes who demand maximum performance out of their shoes. What "tunability" is provided by the prior art requires a complex trade off between all of the elements of the shoe including the outsole, the midsole, and structural members that make-up the shoe, and must normally be done at the design stage, and cannot be varied by the customer.
Accordingly, a need remains for a light-weight shoe that minimizes the material in the sole, adequately supports the foot, and which can be readily customized for an individual's foot or for a particular activity.